mdframed package conflicting with \bgroup, \egroup

I'm using XeLaTeX because of language problem.

The following code has no problem:

\documentclass{article}

%\usepackage{mdframed}

\newenvironment{mynote}{\footnote\bgroup}{\egroup}
\begin{document}
Hello\begin{mynote} world\end{mynote}.
\end{document}


However, the following code gives an error:

\documentclass{article}

\usepackage{mdframed}

\newenvironment{mynote}{\footnote\bgroup}{\egroup}
\begin{document}
Hello\begin{mynote} world\end{mynote}.
\end{document}


What is the reason for the error and how can I resolve it?

-
\footnote, in LaTeX, can't be followed by \bgroup in order to build its argument. If it appears to work is just by chance and it will be typeset incorrectly anyway. – egreg Jun 3 '14 at 20:43
The reason why this fails with mdframed is because the package adds code to \begin and \end. But trust me: your mynote environment doesn't work correctly. – egreg Jun 3 '14 at 20:48

With environ you can define an environment which collects the body for later use.

\documentclass{article}
\usepackage{mdframed,environ}
\newsavebox\NBox
\NewEnviron{mynote}{\footnote{\BODY}}

\begin{document}
Hello\begin{mynote} world\end{mynote}.
\end{document}

-
Thank you. Your solution resolved the problem. However, I still wonder why the second code have not worked... – seoneo Jun 3 '14 at 20:59